Wellbores are sometimes drilled into subterranean formations that contain hydrocarbons to allow recovery of the hydrocarbons. The formation materials encountered while drilling into a subterranean formation can vary widely depending on the location and depth of the desired reservoir. One commonly encountered material is shale, which is generally comprised of various clays. Shale hydration, commonly seen when ordinary water-based fluids are used in water-sensitive formations, can be a significant cause of wellbore instability. Further, the clays forming the shales also tend to adhere to the drill bit or to the bottomhole assembly, severely impairing the rate of penetration during drilling. In some worst case scenarios, failure to remove hydratable clay from the wellbore can lead to gumbo attacks, packing off, lost circulation, and/or stuck pipe.
One common solution used to prevent the shale interaction with water is to use an oil-based drilling fluid, such as an invert emulsion fluid. These fluids have generally performed well as drilling fluid for water-sensitive formation such as those containing shales. However, oil-based drilling fluids can be expensive and less environment friendly when compared to water-based or aqueous based drilling fluids.